A vehicle is typically provided with a cooling system in order to maintain an optimal temperature of a fuel cell stack, an inverter, a motor, an engine, and/or other electric equipment that generates heat during operation. Such a cooling system may be an air-cooled type that cools a heat source by introducing external air to the heat source, or a water-cooled type that circulates a coolant to cool the heat source. Typically the air-cooled type is inferior in cooling performance to the water-cooled type, and thus water-cooled cooling systems are widely employed for vehicles.
During operation of the cooling system for a vehicle, temperature and pressure of a coolant frequently changes according to heat generation amounts of the heat source and operating states of parts such as a pump and valves which control a flow of the coolant. When a pressure or temperature of the coolant becomes beyond, or outside of, an admissible range of a particular part, durability of the particular part may be deteriorated and decrease a lifetime of the part, thereby incurring undesirable effect such as increased friction, noise and costs. For example, when a heat generation amount of a heat source is abruptly decreased, a pressure of a coolant may be abruptly decreased. When a rotating part, such as a pump, rotates at a high speed at such a state, bubbles may be formed in the coolant by a cavitation phenomenon, thereby causing damage to the part by high speed collisions of the bubbles with surfaces of the part.
Therefore, it is desirable that a cooling system may be designed to optimally control an operating pressure of a coolant in order to improve operating lifetime and quality of the cooling system.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.